The long term goal of this project is to understand the molecular mechanisms of human copper homeostasis in atomic detail. A new class of chaperone proteins which function in the intracellular delivery of copper to specific target proteins has recently been discovered. We have crystallized the yeast copper chaperone protein Lys7 which transports copper to SOD1, a cytoplasmic form of superoxide dismutase. The Lys7 crystals, which belong to space group P212121, grow to maximum size of 0.03 x 0.10 x 0.25 mm and have unit cell dimensions 53.2 x 88.7 x 111.1 E. Because the crystals are very thin and diffract weakly using a rotating anode, we have not been able to collect useful data in our laboratory. At SSRL, we plan to collect a complete, high quality native data set, to collect data on crystals derivatized with mercury and platinum compounds, and to collect data on Lys7 in the presence and absence of copper. The three-dimensional structure of Lys7 will reveal the details of copper binding, including stoichiometry and coordination geometry, and will elucidate how Lys7 interacts with SOD1 as well as features which render Lys7 specific for SOD1. This information will represent a significant contribution to a rapidly growing and novel area of bioinorganic chemistry and cell biology.